1. Field of the Invention
The invention relates generally to disk drives and more particularly to an expandable gasket that seals the disk drive's head/disk assembly.
2. Description of the Prior Art
Generally, industrial gaskets are stamped from a sheet of material suitable for their intended application. A stamping apparatus may include a die configured in a predetermined geometry such that when mated with a sheet of gasket material, an image of the die geometry will be punched thereon. The sheet of gasket material may then be further processed to separate the stamped die image from the sheet of gasket material, wherein the remainder of material is conventionally discarded. Gaskets are fabricated in a multiplicity of geometries and hence there must be a corresponding number of die geometries. Depending on the particular application, sheet material selected for a gasket can be relatively expensive, and it becomes useful to minimize waste.
As illustrated in FIG. 1 a hard disk drive head disk assembly ("HDA") 1 includes a base 2 and a stamped, conformable top cover 3 for enclosing the base 1 along with delicate internal components 4 comprising a head-disk interface. The top cover 3 is conformably mated with the base 2, and a gasket 5, FIG. 2, is placed between facing edges of the cover 3 and base 2 to form an air tight seal, isolating the disk drive's internal components 4 from any contaminants present in an environment external to the head disk assembly 1. In disk drive technology, it is critical to maintain a contaminant-free operating environment within the head disk assembly 1, so that contaminants, particularly microscopic particles, do not come between the flying head and the disk storage surface.
In assembly of die-cut sheet gaskets 5, it is not uncommon to use vacuum fixtures, such as the fixture 6 shown in FIG. 3. In this example the fixture 6 may be milled from a block of aluminum alloy. The block 6 includes a milled recess 7 closely matching a final design outline of the gasket 5. The milled recess 7 also defines a series of small holes which lead to an interior hollow plenum in communication via a fitting and suitable conduit with a vacuum source, such as a vacuum pump (not shown). This arrangement enables the recess 7 to be de-pressurized relative to ambient air pressure, thus sucking the gasket 5 firmly into the milled recess 7 and holding the gasket flat within the recess. Once the gasket 5 is positioned and held in place on the fixture 6 by vacuum suction, a paper release liner covering an adhesive coating on an upward-facing surface 8 of the gasket 5 is removed (or an adhesive coating is applied to the surface 8), and the cover 3 is lowered into position over the gasket 5. Preferably, tooling pins or features on the fixture 6 (not shown in FIG. 3) aid in precisely aligning the cover 3 relative to the fixture 6 and gasket 5. Once the gasket 5 is affixed to the cover 3, vacuum is removed from the fixture 6, and the cover-gasket assembly is then removed and ready for installation onto the base 2. In an automated assembly process, the fixture 6 would be upside down, compared with the FIG. 3 orientation, so that the fixture 6 could robotically remove the adhesive-coated gasket 5 from a carrier sheet using vacuum, move the gasket 5 to the cover 3, press the gasket 5 into place on the cover, then release the vacuum, and recycle for the next automated gasket-handling operation.
In the case of disk drive gaskets 5, materials chosen for the gasket are typically characterized by low outgassing, low compression set, and a general compatibility with disk drive internal components. Consequently, materials such as Poron (.TM.) high density polyurethane foam are preferred materials. However, as mentioned, such materials can be relatively expensive. As will be appreciated from the FIG. 2 example, the disk drive gasket 5 is characterized as having a narrow band geometry, generally following an outer edge having narrowed regions 13 of the cast "deep dish" base 2, which encloses a relatively large space. Thus, waste and discard of the majority of unused remaining material after gaskets 5 have been punched and separated from their respective sheets is expensive and undesirable. In addition, Poron (.TM.) high density polyurethane can be environmentally harsh due to its non-biodegradable characteristics. By way of example, a series of substantially circular gaskets stamped from a sheet of gasket material according to the aforementioned process would yield a series of circular gaskets, however, the majority of the surface area of the initial sheet of gasket material including the area positioned inside and outside of the stamped circular rings would typically be discarded.
One method for conserving gasket sheet material is to lay out the gasket patterns in an optimum fashion on the sheet of gasket material. Another method of maximizing the usable surface area of a sheet of gasket material is shown in FIGS. 4a, 4b, and 4c, which illustrate steps of selecting predetermined reconfigurable die geometries as to maximize the number of gaskets realized from a sheet of gasket material. In order to accomplish the aforementioned, gaskets can be stamped from a sheet of material such that a secondary separation and expansion operation is required to configure the gasket into its final form. Specifically, a typical gasket 10 intended to seal the cover or door of an electrical enclosure is initially die stamped from a sheet of gasket material, leaving several strip-like segments 11 connected by "live hinge" regions 12. The gasket 10 is then subsequently unfolded into its final gasket form, which is somewhat analogous to a picture frame. However, after being expanded into a final geometry, the gasket can exhibit severe local deformations in the live hinge corner regions 12. Moreover, as a result of theoretically infinite stresses at the live hinge corner regions 12 caused by the deformations, the gasket material may tear, and consequently not atmospherically seal the enclosure from the outside environment. In some instances atmospheric isolation is not relevant. However, as already explained above, sealing the interior of a disk drive from minute atmospheric particles is critical to proper functioning of the unit.
Therefore, there is a hitherto unsolved need for a gasket design and method that maximizes the number of gaskets realized from a sheet of gasket material, thereby minimizing material waste. There also exists a need for gasket that can be expanded to a desired shape without substantial deformation in order to seal e.g. the HDA of a disk drive from atmospheric contaminants.